In June 2010, a white tiger pair (Anu and Bhishmar) at the Arignar Anna Zoo in Vandalur, India, had their 2nd litter of 3 white tiger cubs. One of these cubs was different – his
white coat appeared to be turning black! As the cub, Sembian, matured,
it became apparent that the blackness was due to an expansion of the
normal black stripes, termed “abundism” or more popularly called
“pseudo-melanism”. Sembian’s coat had a white background with an
over-abundance of blackness – his black stripes were so wide they ran
together in places. [1]

In July 2014, it happened again, this time at the Nandankanan Zoo in Orissa, India, and this time the litter of 4 was a mixture of white and orange cubs born to Sneha and Manish, a white mother and orange father. Two cubs, 1 white and 1 orange, had the overabundance of black stripes . In May 2016 another pair at the zoo – Renuka and Samrat – had one pseudo-melanistic cub (stillborn). In August 2016 the first pair had another litter of 3 cubs – again, one cub was pseudo-melanistic. [2]

At first, the “black” cubs were thought to be “accidents” of nature, or “mutants” – but after the 2016 litters the zoo realised they were dealing with normal genetic inheritance.

The Theory

Pseudo-Melanistic white tiger at Nandkanan Zoo. Pseudo-melanism in tigers appears to be caused by a recessive gene – similar to the white gene, but separate from it as it can affect both white and orange tigers. This would mean that a “normal” orange or white tiger can carry the melanistic gene in a hidden state, as it is masked by the dominant allele.

So assuming it is an inherited trait, a trace of the pseudo-melanistic tigers’ pedigree should give us a clue where it came from. This leads back to 5 wild-born ancestors that all the melanistic cubs have in common: Mohan and Begum of the Rewa line, and Pradeep, Sikha and Rani of the Orissa line. [3] It is highly unlikely that the gene came from the Rewa tigers, as it should have shown up earlier during the inbreeding that occurred in the first few generations of that line. That leaves the 3 from the Orissa line, and a glance at the origin of these 3 tigers shows an obvious candidate : Rani.

Rani, an orange tigress, and one of the founders of the Orissa line of white tigers, was found wild in the Similipal forests in 1967, as a little 7wk old cub. [4]

Location of Similipal Forests.Source: Google Maps

The Similipal Tiger Reserve had for many years been rumoured to harbour “black” tigers, – rumours that were widely dismissed as myth until 1993 when proof was obtained (the skin of a slain tiger). [5] Since then these pseudo-melanistic orange tigers have been photographed by camera traps in the reserve, and it was estimated that there were 3 of them living there in 2014. The Similipal tiger population is threatened, with only an estimated 26 tigers left there in 2016. [6]

Back in 1975, in the Nandankanan zoo, Rani the Similipal tigress mated with Deepak, an orange male who was later found to carry the white gene. Apparently Rani passed the melanistic trait on to her daughter Ganga (also a white gene carrier), who then passed it on to one or more of her many cubs.

Throughout the next 3 or 4 generations, the recessive melanistic gene gradually spread unnoticed throughout the Nandankanan tiger population, until finally 2 melanistic gene carriers were paired together.

Meanwhile, in 1999, Laxman, a white male tiger from the Orissa line, was sent to the National Zoological Park in Delhi to breed with their Rewa line white tigers. Laxman was also descended from Rani, and it is possible that he carried the melanistic gene and passed it to some of his descendants, including Anu and Bhishmar, who became the parents of the blackened Sembian. [note i]

There have been too few melanistic births to be certain which of Ganga’s offspring carried the trait, as it is not likely she passed it to all her cubs. A study of the full birth charts shows the most likely option to be Debabrata plus either Pinaki or Jamuna.

This abbreviated chart above shows the possible line of inheritance. Please note that this chart does not show all the generations and tigers involved. For full (and complicated!) details please refer to the ancestry charts in White Tigers Today..

Is it Caused by Inbreeding?

Kenny the Deformed white tiger, believed to be a victim of inbreeding. photo uncredited

Inbreeding is one way that a recessive trait can show up. However, the expression of a recessive trait does not automatically signify inbreeding, but simply that a trait has had time to be distributed throughout a population unnoticed (because it is masked by the dominant allele).

This late showing of a recessive trait that has been present in the captive population since 1967, illustrates how careful the zoos have been to avoid close inbreeding in the Orissa line of white tigers. [note ii]

It has taken all this time for the gene(s) to spread throughout the population – the Nandankanan pseudo-melanistic cubs are 4 generations removed from any common ancestor, and SIX generations removed from the presumed origin, the tigress Rani.

Significance for White Tigers and Tigers in General

Occurrence of White Tigers in the Wild

This concept of a recessive trait spreading unnoticed throughout a population (see above) is also important in understanding the occurrence of white tigers
in the wild. They did not just pop up here and there spontaneously – 1
in 10,000 – as often suggested, but the hidden white gene seems to have
spread from NE India through to Central India, in time becoming so
common in some areas that white tigers were born more frequently in
these areas – eg Rewa and Bihar. [7]

Captive Populations Preserving Genetic Diversity

As Rani’s daughter Ganga also carried the white gene (from her father
Deepak), she was bred extensively and has many descendants in the
captive population today. In the effort to preserve the white gene, the
zoos have inadvertantly also preserved other tiger genetic diversity
that is endangered in the wild. The pseudo-melanistic trait is a visible
example of this, but there is likely much more variation thus preserved
that we cannot see with the eye.

Today only the orange-with-black-stripes variety remains in the wild
with any regularity, causing many people in the current generation to
believe that they are the only “real” tigers, and that all others are
mythical or man-made. The reality is that these beautiful
orange-and-black tigers are merely the remnants of the once large and
highly diversified tiger population that included many different coat
variations.Conclusion

The pseudo-melanistic trait arose naturally in the wild, where it apparently survives only in Similipal today.

Fortuitously, one tigress from this area was taken into captivity 50 years ago and bred, thus preserving some of the unique genetic diversity of the tigers from that area.

It is highly likely that Rani, the little wild cub from Similipal, carried the pseudo-melanistic trait and passed it on to her daughter Ganga, who passed it on to one or more of her own cubs.

As the Simlipal population is currently threatened, this is another instance of captive tigers (both white and orange) serving as a reservoir of genetic diversity that is endangered in the wild. Notes

[i] Amongst Anu and Bhishmar’s 13 cubs there were no other
reported melanistic cubs. This might indicate that there are other
factors influencing or suppressing the trait.

[ii] There was only one father-daughter pairing, that
of Deepak to Ganga. Offspring were then outcrossed to the unrelated Rewa
line, and I have not found any further parent-child or sibling pairings
at Nandankanan. In recent years they have also outcrossed to wild
tigers, thus strengthening their gene pool further.

The initial breeding of Ganga to her father Deepak would not have
produced pseudo-melanistic cubs as we assume that only Rani (not
Deepak) carried the gene, which she then passed to her daughter Ganga.

No comments:

About Me

This is a blog about what interests me. Here you will find stories on animals, including animal rights material, cute stuff, and random informative posts about weird, beautiful and interesting creatures. Horses, Spotted Hyenas, and Border Collies will make regular appearances.
Also prominently featured will be posts about the Arts. Animation, photography, and the traditional forms, plus "outsider art," film and books.
Other things that will surface here are Japan & the Japanese, John Oliver, surfing, skateboarding and My Little Pony: Friendship Is Magic, interesting places and structures,and my own art, writing and photography.
There will be rants. It's an election year, and I am beginning to have a political dimension to my personality. I am also horrified at the level of injustice and violence visited upon people here in the US and elsewhere - particularly against people of color, immigrants, and the LGBT community. Some of these stories will be very hard to read, but I believe we must read them to keep ourselves mindful of the racist and vicious things that happen every day, to speak out when we see discrimination, and root out its evil from ourselves.